The present invention is broadly concerned with an improved roof deck system for quiet buildings. More particularly, it is concerned with a multilaminate acoustical deck supporting an outer layer of roofing shingles without the need for a metal decking substrate or venting.
The roof of a building normally consists of a waterproof outer layer or membrane of roofing material installed over a supporting deck. Skeletal framing or support members are used to support the deck. The roof deck must be strong enough to support the roofing membrane material as well as any rain or snow load. The roof deck must also remain rigid despite cyclical changes in temperature and varying wind conditions, since any movement of the deck may cause buckling or tearing of the overlying roofing material.
Any of a number of materials may be employed as decking materials, including wood, concrete, gypsum and steel. Steel decking is one of the most common roof deck materials employed in structural steel or masonry framed buildings with open web steel joists. The popularity of steel decking may be attributed to its suitable characteristics with regard to live load, span, fire rating, compatibility with electrical and telephone circuits and ceiling materials, and its relatively low cost. Steel decking is generally available in the form of corrugated or ribbed panels or sheets that are usually attached to steel framing members by welding.
However, despite its many desirable characteristics, steel has a relatively high coefficient of thermal expansion when compared with some other roof substrate materials such as wood and gypsum. As the cycles of the sun increase and decrease the heat load, or the ambient temperature surrounding a building changes with weather and the seasons, steel decking expands and contracts in accordance with this thermal expansion coefficient. Wind and air pressure changes may also cause movement of the decking. Such movement is well known to generate noise. Manufacturers of roofing materials have identified a number of different loci of steel deck/roof structure movement that contribute to noise that can be heard inside a building: the exterior perimeter framing of the roof may move with respect to the steel deck; the deck may move with respect to the underlying steel bar joists; the ends and/or side laps of individual decking panels may move against each other; the deck may move against any of its fasteners; the deck may move with respect to any insulation that has been used; when thermal expansion of decking framed to rigid walls or framed into walls on an angle is added to axial compression loads, compressive flange buckling can result, and purlins in prefabricated structures may move.
Movement of the steel decking substrate of a roof can generate sharp loud noises such as hammering, banging, pops, creaks and booms. In addition, in large clear span structures, the roof deck functions as a diaphragm or sound board (tympanum) which serves to reverberate sounds into the building space below. The resulting noises are particularly undesirable in normally quiet building spaces such as libraries, schools, churches and chapels, auditoriums and theaters. These noises may also be disruptive at certain times in non-quiet building spaces such as gymnasiums, civic centers and arenas. Such noises have been known to substantially impair the utility of the affected building space. When that occurs, they give rise to disputes between builders and clients and may necessitate costly remedial measures.
Various attempts have been made to increase the sound-absorbing or dampening properties of steel decking. For example, steel decking has been fabricated to include perforated fins for receiving insulation. Rigid insulation board has been applied directly over the decking. Cellular steel decking has been fabricated to include perforated bottom panels that serve as a substrate for added insulation. So-called acoustical metal deck has been constructed with open sided flutes or perforations in the ribs or flutes. Noise gaskets have been employed to isolate the structural supports from the steel roof deck. Gaskets have also been employed to isolate the individual corrugated deck sheets at their overlapping side edges and overlapping or butting end joints, so that they do not contact the adjacent deck sheets. Sheets of sound dampening material have been inserted between the steel deck and the roof insulation. Batts of fiberglass insulation have been installed between the upper surface of acoustical ceilings and the lower surface of the steel decking. Termination supports have been modified to include perimeter expansion relief, and expansion runs have been limited to twenty feet. Steel drive pins and screws have also been used to replace welding of steel deck sheets to the underlying steel support structure.
None of these approaches has been entirely successful in eliminating steel roof deck noises in quiet buildings, and most add substantially to the cost of the affected construction project. It is possible to eliminate the steel roof deck entirely, but a substitute diaphragm must be provided. This diaphragm must be capable of meeting shear requirements by transferring horizontal wind and seismic loads to the shear walls as well as supporting the roofing membrane material. Wood ply panels by themselves are generally not well suited for use as a substrate for commercial buildings because wood is subject to shrinkage, swelling, warping, twisting, rotting and burning. Because wood ply panels are subject to movement, they also do not retain fasteners well. Composite roof deck systems are available that include a sound insulating material sandwiched between various wood-based substrates that are somewhat less subject to the problems associated with wood ply panels. Some of these systems are constructed without a metal decking substrate. In such systems, many of the loud noises attributable to thermal expansion load are eliminated. In addition, the insulating layer of such systems serves to dampen noise. Such systems are not weatherproof and are designed for use in association with a roofing membrane material that renders the roof impervious to the weather.
Composition shingles are a particularly favored roofing membrane material because they are relatively light weight, easy to install, durable and esthetically pleasing. They are a particularly economical choice for use in large, long span buildings. However, when composition shingles are applied over a wood-containing decking substrate, such as a composite roof deck system, it is necessary to provide venting underneath the shingles to prevent cracking or splitting of shingles and to maintain the decking in a dry condition. It is difficult to provide effective venting beneath shingles, and such venting is generally accomplished by constructing a series of venting channels and spacers between the decking substrate and the shingles. Because the open ends and empty spaces of the channels provide access to insects and nesting spaces for animals, screen covers are generally installed over the ends of the channels. Thus, the venting requirements for composite roof deck systems with wood based substrates make it difficult and expensive to install a composition shingle roofing membrane over currently available systems.
Consequently, there remains a need for a roof deck system that is suitable for use in quiet buildings, that does not require the use of a steel deck substrate, and that can accept a composite shingle membrane material without the need for a venting system.